Copper Oxide and Titanium Dioxide Nanoparticle-Modified Etch-and-Rinse Adhesives with Photoactivation: Effects on Bonding Performance to Caries-Affected Dentin

This study evaluated and compared copper oxide (CuO) and titanium dioxide (TiO2) nanoparticles (NPs) incorporated into etch-and-rinse adhesives, with and without photoactivation, on microleakage (ML), resin tag length (RTL), micro tensile bond strength (μTBS), and degree of conversion (DC) in caries-affected dentin (CAD). One hundred thirty extracted permanent mandibular molars with occlusal caries (ICDAS 5) were randomly allocated into five groups (n = 26): unmodified adhesive (control); CuO NP-modified (1 wt%); CuO NP-modified with green-light activation; TiO2 NP-modified (1 wt%); and TiO2 NP-modified with UV pre-irradiation. Modified adhesives were applied in etch-and-rinse mode and LED-photopolymerized. Micro-hybrid composite build-ups were placed incrementally, and specimens were thermocycled. ML was assessed by dye penetration, RTL by SEM, μTBS by universal testing machine, and DC by ATR-FTIR; fracture modes were classified as adhesive, cohesive, or admixed. Data were analyzed using one-way ANOVA and post hoc Tukey’s. All experimental groups outperformed the control for ML, RTL, and μTBS (p < 0.05). For DC, only the photoactivated groups exceeded control (75.23% and 76.12% vs. 65.22%; p < 0.05); whereas, the non-activated nanoparticle groups did not differ from control. Pre-irradiation of NP-modified adhesives before photopolymerization produced better bonding and marginal sealing, a promising strategy for resin composite restorations.